How to Placing Concrete in Molds and Curing for Standard Cylinder Test
To place the concrete in the cylinder molds, for the molds with a diameter of 100 mm, height 150 mm, place concrete into two equal layers. After placing the first layer, take a round steel bar with a diameter of 10 mm or 16 mm to rod the concrete 25 times and knock with a rubber hammer on outside molds 10 to 15 times, then place the second layer and do the same as the first layer, but the rodding should be inserted into the first layer to a depth of 25 mm. For molds with a diameter of 150 mm and a height of 300 mm, it is placed in three equal layers, each layer is done in the same way as a small mold. The specimen for bending test is placed in two equal layers, one time rod for the area of 14 square centimeters.
Removal of molds should be done within 24 to 32 hours after placing and then curing them by soaking in water at a temperature of 23 degrees Celsius plus/minus 2 degrees Celsius. We need to add the Calcium Hydroxide into water at the amount of 3g/L to prevent the strength loss of concrete.